This invention relates to a polyolefin composition which contains a polyolefin and at least one unsaturated compound in an amount effective to impart resistance to the deleterious effects of sterilizing radiation upon the polyolefin, as well as articles produced from the composition.
Polyolefins, and in particular, polypropylene, have been used to manufacture articles, such as medical devices and food packaging, which are subjected to ionizing radiation to sterilize them. However, such articles tend to become brittle upon exposure to such high energy radiation. This problem becomes more severe as the surface area of the article increases. Thus, fiber and films are particularly susceptible to embrittlement.
The prior art has attempted to overcome this problem by adding various stabilizers to the polyolefin. For example, U.S. Pat. No. 4,110,185 to Williams et al discloses the addition of a non-crystalline mobilizing additive to a semicrystalline polyolefin generally. The mobilizing additive is said to increase the free volume of the polymer, and may be selected from hydrocarbon oils, vegetable oils, silicon oils and low molecular weight non-crystalline polymer greases. U.S. Pat. Nos. 4,274,932 and 4,467,065, both to Williams et al, disclose the addition of the mobilizing additive to a semi-crystalline polyolefin having a narrow molecular weight distribution. U.S. Pat. No. 4,749,734 to Williams et al discloses incorporating a heterocyclic hindered amine and the mobilizing additive. These patents do not distinguish between saturated and unsaturated compounds with respect to this mobilizing additive.
U.S. Pat. No. 5,041,483 to Burch discloses the use of cyclic unsaturated rosin esters as odor-suppressing stabilizers for polypropylene compositions. Aliphatic unsaturated compounds are not disclosed.
U.S. Pat. No. 4,888,369 to Moore, Jr. proposes the addition of a synergistic mixture of a hindered amine, a hindered phenolic and a phosphorous-containing compound to polypropylene.
U.S. Pat. No. 5,376,716 to Nayak et al. discloses the addition of triallyl trimellitate to polypropylene or propylene-ethylene copolymers to produce a radiation resistant resin blend.
European Patent Publication No. 7,736 to Rayner et al. discloses that the resistance of polyolefins to the discoloration which occurs as a result of gamma-irradiation could be improved by incorporation of one or more specified hindered amines. U.S. Pat. No. 4,563,259 to Rayner discloses a composition comprising a substantially crystalline polyolefin having a molecular weight distribution ratio of 7.0 or below and containing from 0.1 to 2 weight percent of a hindered amine or its salt. The mobilizing additive of U.S. Pat. No. 4,274,932 can optionally be incorporated into the composition.
U.S. Pat. No. 4,797,438 to Kletecka et al. discloses stabilizing polypropylene using a hindered amine containing a polysubstituted piperazin-2-one moiety or a polyalkylene polyamine having pendant substituted oxo-piperazinyltriazine moieties.
U.S. Pat. No. 4,594,376 to Hamada discloses a propylene polymer composition containing 0.5 to 2 parts by weight of triallyl (iso)cyanurate and/or diallyl(iso)phthalate and, optionally, an organic peroxide.
U.S. Pat. No. 4,822,666 to Hudson discloses a non-woven polypropylene fabric stabilized against ionizing radiation by a long chain aliphatic ester added to the polypropylene prior to formation of the fabric. A specific benzoate ester, hexadecyl 3,5-di-t-butyl-4-hydroxybenzoate, is preferred.
U.S. Pat. No. 5,140,073 to Rolando et al. proposed blending non-crystalline mesomorphous polypropylene and a polymer compatible with the polypropylene, such as polybutylene, rather than adding a non-polymeric radiation stabilizer to the polyolefin.
U.S. Pat. No. 4,431,497 to Rekers discloses polyolefin compositions stabilized with from about 100 to about 10,000 ppm of a stabilizer selected from benzhydrol or a benzhydrol derivative of specified formula.
U.S. Pat. No. 4,710,524 to Donohue discloses polyolefin compositions stabilized with a hindered piperidine compound and another stabilizer additive, preferably a benzophenone precursor.